The present invention pertains to RF (radio frequency) circuitry and more particularly detection of circuit failures and protection of RF amplifiers and the RF path due to overloading caused by circuit failure.
When circuitry associated with an RF power amplifier fails, such as PIN diode switches, harmonic filters or power sensors, the automatic level control (ALC) loop that controls the power amplifier output level becomes an open loop. The result of this type of component failure is that the power amplifier attempts to deliver maximum power output into the failed circuitry. One result of this failure may be that various components are damaged by the power overload. More extensive damage may result from damage to the printed circuit board on which the components are mounted. Printed circuit board damages are very expensive to repair or in some cases non-repairable.
In the open loop situation (when a malfunction occurs), the ALC demands maximum power. As a result, the components become thermally damaged.
It is highly desirable therefore to provide a RF power amplifier overload protector and method for monitoring the RF power output of a power amplifier of a transmitter and detecting a malfunction of this type and turning off the power amplifier.